1. Field of the Invention
The present invention relates to a motor-fan assembly and a combustion-type power tool, such as nail gun, employing the same.
2. Description of the Related Art
A fan for agitating a gaseous matter or mixing two or more kinds of gaseous matters has been used in a variety of situations. Typically, a motor is a source for driving the fan. Attachment of the motor shaft to the fan has conventionally been made as shown in FIG. 1.
FIG. 1 is a partial cross-sectional view showing a conventional motor-fan assembly. A motor 9a is accommodated in a casing 9c. The casing 9c is formed with a hole 9d for allowing the motor shaft 9b to pass therethrough. The motor shaft 9b protrudes outward from the casing 9c through the hole 9d. A fan 8 is fixedly attached to the tip end portion 9e of the shaft 9b. The tip end portion 9e of the shaft 9b has a D-shaped cross-section. Specifically, a flat portion 9f is formed on the outer periphery of the shaft 9b to extend in a longitudinal direction of the shaft 9b. 
As best shown in FIG. 8, the fan 8 has a hub portion 8b and a plurality of blades 8a (four in the illustrated example) extending radially outwardly from the hub portion 8b and also equally angularly spaced apart from one another around the hub portion 8b. A center hole 8c is formed in the hub portion 8b. 
A connection block 11 is used to connect the motor shaft 9b and the fan 8. FIGS. 2 through 5 show the connection block 11, in which FIG. 2 is a top view, FIG. 3 is a cross-sectional view cut along the line III-III in FIG. 2, FIG. 4 is a side view, and FIG. 5 is a bottom view. The connection block 11 is an intermediate member disposed between the motor shaft 9b and the fan 8. Specifically, the motor shaft 9b is secured to the connection block 11 and the fan 8 is fixed to the connection block 11.
As shown in FIGS. 2 and 3, a through-hole 11a is formed in the connection block 11 for allowing the motor shaft 9b to be inserted thereinto. A lateral hole 11d is also formed in the connection block 11. The lateral hole 11d is open to the outer periphery of the connection block 11 and extends perpendicular to the direction in which the through-hole 11a extends. The lateral hole 11d extends to reach the through-hole 11a. A female screw 11b is threaded in the inner periphery of the hole 11d so that a male screw 12 can threadingly engage the female screw 11b as shown in FIG. 1.
To assemble the motor 9 and the fan 8 using the connection block 11, the fan 8 is firstly attached to the connection block 11 by caulking. FIG. 6 shows the fan 8 and the connection block 11 before caulking, FIG. 7 shows the fan 8 and the connection block 11 after caulking. FIG. 8 is a bottom view showing the fan 8 caulked to the connection block 11. As shown in FIGS. 3 and 8, the connection block 11 is provided with a plurality of caulking pieces 11c (eight in the illustrated example) at the lower peripheral portion of the connection block 11. The caulking pieces 11c are equally angularly spaced apart from one another around the lower periphery of the connection block 11. As shown in FIG. 6, to place the connection block 11 and the fan 8 in an assembling state, the caulking pieces 11c are slided down along the inner wall of the center hole 8c of the hub portion 8b until the caulking pieces 11c protrude outwardly from the center hole 8c. Then, the caulking pieces 11 are bended radially outwardly, whereby the fan 8 is attached to the connection block 11.
To attach the motor shaft 9b to the connection block 11 with the fan 8 attached thereto, the motor shaft 9b is inserted into the through-hole 11a of the connection block 11 while directing the flat portion 9f of the motor shaft 9b toward the lateral hole 11d. The male screw 12 is threadingly engaged with the female screw 11b formed in the lateral hole 11d. The male screw 12 is advanced deeper until the tip end thereof is brought into abutment with the flat portion 9f of the shaft 9b. Abuttment of the male screw 12 with the flat portion 9f fixedly attaches the motor shaft 9b to the connection block 11 and prevents the motor shaft 9b from detaching from the connection block 11 during rotation.
One problem with the above-described conventional motor-fan assembly is that formation of the flat portion 9f on the motor shaft 9b requires a special machining, which causes an increase of cost in manufacturing the assembly. Another problem is that the male screw 12 and the lateral hole lid for accepting the male screw 12 are unsymmetrical elements in the assembly, causing rotational balance of the fan 8 to degrade. When vibrations of the motor shaft 9b occur as a result of the rotational imbalance of the fan 8, the motor shaft 9b may contact the hole 9d of the motor casing 9c during rotation As a result, the service life of the motor 9a is shortened.